VARIETIES OF MANKIND. 



1303 



degree of change -which does take place in 

 the several races of mankind, between infancy 

 and old age, there is seldom much difficulty 

 in collecting information. 



2. The influence of external conditions in 

 modifying the conformation hoth of Plants 

 and Animals, is a question of fundamental 

 importance in the determination of the value 

 of specific characters. In this respect there 

 is a very extraordinary diversity among the 

 several races of living beings, even among 

 those which are most nearly allied to each 

 other ; for whilst some possess such a capacity 

 for variation, that they are easily influenced 

 by changes in external conditions, and can, in 

 consequence, readily adapt themselves to 

 these, to others this capacity seems altogether 

 denied. It is from this circumstance that we 

 find particular species, of plants, as well as of 

 animals, restricted to particular conditions in 

 regard to climate, food, &c., their constitu- 

 tions not being able to adapt themselves to 

 any considerable change ; whilst others are 

 more widely dispersed, simply because their 

 constitutions can accommodate themselves to 

 alterations in these conditions. Hence a 

 change of food or climate, to which the latter 

 soon become habituated, is fatal to the former. 

 We see this difference well marked in the 

 Feline tribe ; for whilst the greater part of the 

 larger species, such as the lion and tiger, are 

 inhabitants of tropical regions, and cannot 

 endure the winter's cold, even in the temperate 

 zone, the domestic cat follows man in almost 

 all his wanderings, and can sustain extremes 

 of heat and cold as well as he can himself. 

 This accommodation is effected by a change 

 in the organism itself, of which evident 

 indications are frequently presented, even 

 within the course of a short time: thus, sheep 

 transported from this country to the West 

 Indies soon loose their covering of thick 

 wool, and acquire in the place of it a short, 

 fane hair, shining and smooth, like that of the 

 goat in his best state, so that after a few 

 years the sheep can scarcely be distinguished 

 from the goats, save by their general con- 

 formation ; and in this, too, from the usual 

 absence of any considerable accumulation of 

 fat in the bodies of the sheep, there is not 

 nearly so much difference between the two 

 races, as there is in temperate climates. 



The continued action of the same cir- 

 cumstances for a few generations, gives in- 

 creased permanence to the new characters of 

 the breed, so that acquired peculiarities of 

 conformation become congenital. Thus, Sir 

 C. Lyell mentions* that some Englishmen 

 engaged in conducting the mining operations 

 of the Real del Monte Company in Mexico, 

 carried out with them some greyhounds of the 

 best, breed, to hunt the hares which abound 

 in that country. The great platform, which 

 is the scene of sport, is at an elevation of 

 about 9000 feet above the level of the sea, 

 and the mercury in the barometer stands 

 habitually at the height of about 19 inches. 



* Principles of Geology, seventh edit. p. 568. 



It was found that the greyhounds could not 

 support the fatigues of a long chase in this 

 attenuated atmosphere, and before they could 

 come up with their prey, they lay down 

 gasping for breath ; but these same animals 

 have produced whelps, which have grown up, 

 and are not in the least degree incommoded by 

 the want of density in the air, but run down 

 the hares with as much ease as the fleetest 

 of their race in this country. In fact, it can- 

 not be reasonably questioned, if the history of 

 the domesticated races of animals be fairly 

 considered, that changes in external condi- 

 tions are capable of exerting a very decided 

 influence upon the physical form, the habits 

 and instincts, and the various functions of 

 life, in species possessing this adaptiveness. 

 The variations thus induced extend to con- 

 siderable modifications in the external aspect, 

 such as the colour, the texture, and the 

 thickness of the external covering ; to the 

 structure of limbs and proportional size of 

 parts ; to the relative development of the 

 organs of the senses and of the psychical 

 powers, involving changes in the form of the 

 cranium, and to acquired propensities, which, 

 within certain limits (depending, it would 

 appear, on their connexion with the natural 

 habits of the species) may become hereditary. 

 Of the changes in psychical characters thus 

 induced by external circumstances, the fol- 

 lowing are trustworthy examples. We are 

 informed by M. Roulin (to whose researches 

 on the changes which the domesticated races, 

 introduced by the Spaniards into South Ame- 

 rica, have subsequently undergone, we shall 

 frequently have occasion to refer), that a race 

 of dogs employed for hunting deer in the 

 platform of Santa Fe, in Mexico, is distin- 

 guished by the peculiar mode in which they 

 attack their game. This consists in seizing 

 the animal by the belly, and overturning it by 

 a sudden effort, taking advantage of the 

 moment when the body of the deer rests only 

 upon the fore-legs ; the weight of the animal 

 thus thrown over, being often six times that 

 of its antagonist. Now, the dog of pure 

 breed inherits a disposition to this kind of 

 chase, and never attacks a deer from before 

 while running; and even should the deer, not 

 perceiving him, come directly upon him, the 

 dog steps aside, and makes his assault upon 

 the flank. On the other hand, European 

 dogs, though of superior strength and general 

 sagacity, are destitute of this instinct ; and for 

 want of similar precautions, they are often 

 killed by the deer on the spot, the cervical 

 vertebra? being dislocated by the violence of 

 the shock.* A new instinct has also become 

 hereditary in a mongrel race of dogs, employed 

 by the inhabitants of the banks of the Magda- 

 lena almost exclusively in hunting the white- 

 lipped peccari. The address of these dogs 

 consists in restraining their ardour and attach- 

 ing themselves to no individual in particular, 

 but keeping the whole in check. Now, among 

 these dogs, some are found, which, the very 



* Annales cles Sciences Naturelles, 1829, torn, 

 xvi. p. 16. 



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